1. Field: The invention is concerned with devices for implantation or partial implantation in living human or animal bodies.
2. State of the Art: There are currently many devices that have been developed for full or partial implantation into a living body. These include heart pacemakers, pumps for administering medication, electrodes, sensors of various kinds, and attendant electrical leads, catheters, and tubing, for continuously monitoring certain body conditions.
These devices generally have limited life in the adverse biological environment of the body and need to be replaced periodically. However, each time such a device is replaced, it requires major surgery with the accompanying risks.
One reason that replacement of such devices is periodically required is the tendency for materials to build up on or in critical portions of the device, thereby seriously interfering with proper and effective operation. The build-up may be of natural body materials or of materials discharged by the device or it may be a combination or result from an interaction of these. Thus, when a device is implanted, because of the body's tendency to reject or isolate foreign material, body material will start to build up on and around the device.
If a sensor, for example, is placed in the blood stream, the blood will tend to coagulate and build up on the sensing surface. After a period of time, this build-up of material can severely interfere with the operation of the sensor, making replacement necessary. The same problem occurs in other parts of the body with build-up of cells, tissue, and various other materials, such as sheetings of protein. Also, where a membrane or other surface is used for passing only selected molecules, it may become poisoned, i.e., blocked or clogged, by other molecules. Again, with devices other than sensors, similar problems can arise. Such devices are rendered ineffective or inoperable after a period of time by the build-up thereon of foreign materials.
With devices which discharge a material during operation, such as pumps by which medication is continuously or periodically supplied to the blood stream or to other parts of the body through catheters or otherwise, the catheter or other passages often become blocked by precipitation of the material being pumped, by blood clots, or by other build-up, thereby rendering the entire pumping device ineffective or inoperable. For example, with pumps for pumping insulin or other proteins, the material being pumped into the body has a tendency to precipitate in the catheter, thereby clogging it. Also, materials from the device itself, such as gases or other chemicals released over periods of time from materials used in construction of the device, may build up or interact with body materials to thereby interfere with the device's operations. Again, under these conditions replacement of the device is necessary. With devices such as heart pacemakers, neuro-stimulators, or electronic bridging circuits where electrical leads extend from the device to body parts or between body parts, the leads themselves, particularly where they attach to body parts, may be subject to material growth or build-up to the point where conduction between the lead and body part may be seriously affected.
A second reason necessitating replacement of some devices, such as various sensors, is that the devices themselves will degrade or wear out with time, so that operation is no longer satisfactory.
Presently, there is no known way to restore, rehabilitate, clean, or otherwise service a device, whose operation has become seriously degraded, ineffective, inefficient, or has ceased completely, while such device remains in the body.
One of the current pressing needs for appropriate insulin administration is the development of a long term, implantable, glucose sensor. Such a glucose sensor is urgently needed to provide an adequate, closed loop, insulin administration system, as, for example, one in which an implantable insulin pump is used so that insulin administration will closely follow normal body routine. There are currently no glucose sensors available which will maintain sensing ability in vivo for more than a few hours or days. Since replacement of such a sensor on a daily basis is entirely impractical, implantable insulin pumps have had only limited use. However, if a known type of glucose sensor could be restored within the body, extensive use of implantable insulin pumps would become a reality.